(Agencies)
Updated: 2007-11-12 16:36

PARIS - Researchers in the United States believe they have explained how a highly virulent strain of the superbug called methicillin-resistant staphylococcus aureus (MRSA) is able to dodge the immune system.

A registered nurse washes his hands in the sink while attending to patients in an emergency room in Miami, Florida in October 2007. [Agencies]

This strain, called community-associated MRSA, or CA-MRSA, is more vicious than the hospital-borne strain of MRSA, the trigger for a global scare surrounding bacteria that are impervious to all but a handful of antibiotics.

CA-MRSA causes severe skin infections, including "flesh-eating" necrotising fasciitis, and potentially fatal blood poisoning.

It is now the cause of the majority of infections that result in trips to the emergency room in US hospitals, the New England Journal of Medicine reported last year.

Investigators led by Michael Otto of the National Institute of Allergy and Infectious Diseases (NIAD) found that CA-MRSA strains secrete a much higher level of small peptides, or protein fragments, called phenol soluble modulins.

These peptides play a stealthy but important role in helping the bacteria to cause disease by worsening inflamation and killing red blood cells and immune cells called neutrophils, they believe.

They tested their hypothesis on mice. Bacteria that had been genetically manipulated to lack phenol soluble modulins had a far less virulent effect on the rodents.

The study is published online on Sunday in the journal Nature Medicine.

In June, the European Centre for Disease Prevention and Control (ECDC) warned that "healthcare-associated infections" which are resistant to many antibiotics, such as MRSA, are "possibly the biggest infectious disease challenge facing the EU."